Method of operating a respirator and an apparatus for applying said method

ABSTRACT

A respirator for feeding pressurized gas into the lungs during an insufflation phase, after which the gas supply is interrupted and the gas is permitted or brought to escape from the lungs during an exhalation phase, the source of power for the insufflation phase is constituted by compressed gas within a closed chamber having rigid walls and a specific size, said chamber being connected to the lungs during the insufflation phase.

United States Patent Okmian Sept. 2, 1975 [54] METHOD OF OPERATING A RESPIRATOR 3,659,601 5/1972 Bushman 128/ 145.8 AND AN APPARATUS FOR APPLYING SAID 3,762,408 10/1973 Cox 128/1458 METHOD [75] Inventor: Ludvig Georg Okmian, Lund, Primary Examiner-Richard A. Gaudet I w Sweden Assistant Examiner-Henry J. Recla 73 Assignee: AB M.A.U. Medicinsk Audiovisuell Attorney. F"m Ladas Parry Von Goldsmith & Deschamps Undervlsnlng, Lund, Sweden [22] Filed: Dec. 11, 1973 [21] Appl. No.: 423,859 [57] ABSTRACT A respirator for feeding pressurized gas into the lungs [3O] Forelgn Apphcanon Pnonty Data during an insufflation phase, after which the gas sup- Dec. 13, 1972 Sweden 16236/72 p y is interrupted and the gas is permitted or brought to escape from the lungs during an exhalation phase, [52] US. C1.2 l28/l45.8, 128/1458 the source of power for the imufflation phase is com Cl- S tute p e e ga a closed Chamber [58] Field of Search 128/1458, 145622145858, having rigid walls and a specific size Said chamber 128/1422 l being connected to the lungs during the insufflation h [56] References Cited p ase UNITED STATES PATENTS 5 Claims, 4 Drawing Figures 3,556,095 1/1971 1smach 128/1458 P M S Q KRM S q-- K V S V UT PU V PATENTED SEF' 21975 SHEET 2 o 3 KRM \ulllllllnlllllllllll'llll' FIG. 3

PATENTEDSEP 3, 902,487

SHEET 3 3 FIG. 4 K/V cm H2O METHOD OF OPERATING A RESPIRATOR AND AN APPARATUS FOR APPLYING SAID METHOD Already at the beginning of this century artificial respiration was used as a method for ventilating the lungs of patients. The first types of machines foradrninistering artificial respiration were of the type iron lung" in which breathing was effected, by varying the air pressure around the chest of the patient in a rhythmical way.

Alreadyin the. thirties P. Frenckner (Acta Oto- Laryng. 1934, suppl. Bronchial and tracheal catheterization") constructed the first breathing apparatus for insufflating gas into the lungs. The apparatus was marketed by Aga AB and called Spiropulsator. The construction was used substantially as an anaesthetic apparatus in thoracic surgery. Owing to the poliomyelitis epidemics after World War II there was an increased need for breathing apparatuses also outside the operation wards. Constructions such as Lundia, Gothia, Engstriim, Radcliff, Bird and others were put on the market. The number of types of apparatus rapidly increased with the progress in anaesthesiology and the development of postoperative breathing treatment. In a monograph with the title Automatic ventilation of the lungs, written by W. W. Mushin, L. Rendell-Baker and P. W. Thompson, published by Blackwell Scientific Publications, Oxford 1959, more than 250 different constructions are described, among other those mentioned above. After that the number of constructions has increased but of all the more or less ingenious creations only some 20 have found extensive application and have been spread outside the country in which the construction was invented.

The vast majority of respirators have been designed for adult use. The medical development of infant treatment in the fifties and sixties, however, created a great demand for respirators also for infants. To begin with various apparatuses for adults were tried and modified. In recent years now and then constructions for infants only have been proposed (the Loosko and Bird respirators). The difficulty of treating patients of all ages with the same respirator is due to the dosage of respiration. Infants breathe with breaths of 15 to ml while an adult breathes with breaths of 450 to 500 ml. Apart from this the respiration must be adapted to the size of the body, entailing special difficulties with respect to infants since the new-born child will increase his weight by 300 during the first year of his life. Apart from these great deviations between infants and adults there is the difference that children below 2 years of age have a distinctive mechanics of breathing. Among paediatricians who have penetrated into this complex of problems in recent years the opinion has prevailed that it is not possible to cover both infant and adult treatment with one and the same type of respirator.

One object of the invention is to eliminate this drawback and achieve a new method of operating a respirator for the ventilation of the lungs of patients, especially infants, so that by simple adjustment the respirator may be adapted to varying breathing requirements. Another object of the invention is to achievea substantially better economy in the use of breathing gas and to eliminate the insufflation gases, especially anaesthetic gases, emitting fromconventional respirators. A third object is to provide an apparatus for operatingrespirators at a substantially lower cost than what has been possible so far. i

As in the conventional ways of operating a respirator, in the method according to the invention pressurized gas is fed into the lungs during an insufflation phase, after which the gas supply is interrupted and the gas is permittedor brought to escape from the lungs through an exhalation valve during the exhalation phase. The characteristic feature of the method according to the invention, however, is that a gas volume calculated on the basis of a desired insufflation volume of a single breath is compressed in a closed compression chamber having rigid walls to a pressure which is higher than the pressure prevailing at the end of the insufflation phase in a patient connection chamber of a substantially constant volume, which is in open connection with the lungs of the patient and is connected with the exhalation valve, that the closed compression chamber containing the compressed gas volume is connected through an insufflation valve with the patient connection chamber for equalizing the pressures between the compression chamber and the patient connection chamber the exhalation valve being kept closed, and that, after the equalization of pressures between the compression chamber and the patient connection chamber, the insufflation valve is closed and the exhalation valve is opened, through which latter valve the pressure in the patient connection chamber is relieved to the atmosphere, and a compression of a new gas volume for the succeeding insufflation phase is started in the compression chamber. Thus, the method is unique by the fact that the source of power for the insufflation phase is constituted by compressed gas within a closed chamber having rigid walls and a specific size. The desired volume of insufflated gas is determined in a conventional way relative to, among other things, body weight and on the basis of this desired volume of insufflation it may then be easily determined how great the volume of gas should be which has to be compressed in the closed chamber to have supplied exactly the desired volume of gas into the lungs of the patient at the equalization of pressures between said chamber and the lungs. The gas volume which must be compressed in the closed chamber to achieve the desired volume of insufflated gas at a single breath may be varied either by adjusting the pressure to which the gas will be compressed in the closed chamber being of a constant size, or by adjusting the volume of the closed chamber in which the gas is compressed to a predetermined pressure.

Thus, the invention provides a considerable simplification of the construction of the respirator. The invention also relates to an apparatus for operating a respirator by the method according to the invention, comprising an insufflation valve, an exhalation valve, means for supplying pressurized gas to the lungs over an insufflation valve, and. control circuits and means for controlling the operation of the various parts of the apparatus, characterized in that said means for supplying pressurized gas to the lungs comprises (1 a compression chamber having rigid walls, said chamber being connectable, over an inlet valve, with a pressurized gas source and, over the insufflation valve, with the lungs,

(2) a metering unit connected with the compression chamber and adapted to determine the pressure tion valve and a tracheal connection and which is connectable with the compression chamber over the insufflation valve, with the lungs over the tracheal connection and with the atmosphere over the exhalation valve, and that the apparatus is arranged in such away that when the insufflation valve is open the compression chamber is of a fixed volume and the pressure therein is influenced only by the flow through the insufflation valve.

The invention will be more closely described in the following with reference to the enclosed drawings wherein FIG. 1 is a diagram illustrating one embodiment of the apparatus according to the invention;

FIG. 2 is a diagram illustrating another embodiment of the apparatus according to the invention;

FIG. 3 is a graph of the pressure conditions of the apparatus shown in FIG. 1 when operated; and

FIG. 4 discloses diagrammatically an automatic metering system for the apparatus according to the invention shown in FIG. 1.

The apparatus according to the invention illustrated in FIG. 1 has a compression chamber module KRM which comprises a closed chamber having rigid walls and a specific size, so that the volume of this closed chamber will remain constant during the operation of the apparatus. A metering module MM and a patient module PM are connected with the compression module. The inlet of the compression chamber module which is connectable with a pressurized gas source is controlled by an inlet valve KIV while the outlet of the compression chamber and its connection with the patient module is controlled by a separation valve SV which simultaneously operates as an insufflation valve. The patient module has an outlet valve PUV which operates as an exhalation valve and has, furthermore, a tracheal connection T for connection with the lungs of the patient. A maximum pressure valve (not shown), i.e., a safety valve, may be connected in a conventional way with the patient module between the separation valve SV and the tracheal connection T. In the apparatus according to FIG. 1 there is also provided an electronic impulse module EIM which comprises control circuits and an automatic system for controlling and sensing the various components of the apparatus. This electronic impulse module is connected with all three valves KIV, SV and PUV and also with the metering module MM and will determine the operating cycle and rate of the respirator.

The apparatus shown in FIG. 1 will operate in the following way. Initially, valves KIV and SV are closed and PUV open. When the apparatus is started the inlet valve KIV to the compression chamber is opened to connect said chamber with the pressurized gas source, the pressure in the compression chamber increasing to a predetermined value P, (cf. FIG. 3) which is sensed by the metering module MM. When this pressure is reached the metering module will supply a signal to the electronic impulse module which will now close the inlet valve KIV. The apparatus is now ready to be connected with the patient. After the patient has been con nected the separation valve SV is opened, the compression chamber being connected with patient module PM which is connected with the lungs of the patient. The outlet valve PUV of the patient module and also the inlet valve KIV of the compression module are closed at this stage. The result will be an equalization of pressures between the compression chamber KRM and the patient module and the lungs of the patient, the pressure falling to the pressure P (FIG. 3). At this stage the separation valve will be closed and immediately afterwards the exhalation valve PUV and also the inlet valve KIV of the compression chamber will be opened. The opening of the exhalation valve PUV will result in the relief of the pressure of the lungs of the patient to the atmosphere, i.e. the patient exhales. The opening of the inlet valve KIV of the compression chamber will result in resupplying of gas until the pressure P, has been reached again in the compression chamber KRM. After that the valves KIV and PUV will be closed and then the separation valve SV will be opened so that a new insufflation phase will be started.

The various valves may be pressure controlled and/or time controlled. In a preferred embodiment the inlet valve KIV has a time controlled opening process and a pressure as well as time controlled closing process while the two other valves SV and PUV are only time controlled.

The arrows in FIG. 1 indicate the directions of the gas flow in the various parts of the apparatus.

The size of a single breath may easily be determined on the basis of the difference between pressures P, and P on one hand, and the total size of the compression chamber and the patient module on the other hand, the latter being adapted to have a substantially constant volume during the operation of the respirator; it may comprise a tube which is flexible at least at the extreme end of the tracheal connection but the flow channel of which has a substantially constant cross sectional area. The supply of respiration gas to the apparatus is controlled automatically on the basis of the existing rectilinear relationship between volume and pressure change of the apparatus and the desired size of the breath in accordance with known methods, for instance with what is disclosed by L. G. Okmian, Artificial Ventilation by Respirator for Newborn Infants during Anaesthesia, Acta Anaesthesiologica Scandinavica, 1963, vol. 7, p. 31 to 57 (the compression formula and the two-pressure method, p. 34, 35 and p. 46 to 54).

As will appear from FIG. 4 a manometer may be used as the metering module MM, an adjustable impulse generator IG being used to determine the pressure P This impulse generator IG feeds its impulses to a relay in the electronic impulse module EIM which, in its turn, will close the inlet valve KIV when the pressure P has been reached. On the manometer a fixed pressure scale 10 may be arranged and a displaceable scale unit 11 with a scale 12 referring to the kilo weight of the body and another scale 13 referring to the milliliter size of the breath. These two scales l2, 13 should be retrograduated, i.e. graduated in the opposite direction of the pressure scale 10.

In the embodiment of the apparatus according to the invention shown in FIG. 1 the size of a single breath is varied by adjusting the pressure to which the gas is fed into the compression chamber KRM which in this case has a constant volume. However, the same maximum pressure in the compression chamber may be constantly used and instead the size of the compression chamber may be adjusted to vary in this way the size of the single breath. Such a system is shown in FIG. 2 which differs from FIG. 1 only in that the compression chamber KRM has a piston K which by means of a motor M may be adjusted to different positions in dependence of the desired size of the compression chamber for the patient in question. In this embodiment of the apparatus according to the invention the equalized pressure P; will vary as a function of the volume of the compression chamber KRM.

A great advantage of the apparatus according to the invention is that the respirator ventilation of the lungs especially in infants may be controlled in a much more efficient and exact way. In addition one and the same respirator may be adapted for either infant or adult treatment by shifting the compression chamber module. Another salient advantage is that all breathing gas fed into the respirator apparatus may be fully used for its purported end owing to the fact that the gas remaining in the compression chamber module at the end of the insufflation phase is prevented from escaping into the atmosphere during the exhalation phase, which is the case in known respirators. Thanks to this advantage not only a considerably better economy with respect to the consumption of gas will be achieved but also an elimination of the risks of poisoning of the operation staff which are in most cases subjected to considerable quantities of anaesthetic gas during the intervention.

The operation of the apparatus according to the invention will be described in the following with reference to FIGS. 1, 3 and 4. First it is checked that the compression chamber module KRM is of a convenient size with respect to the patient in question so that no unduly high pressure in the compression chamber module is used to compress the required gas volume for feeding into the lungs of the patient. The volume of insufflation may vary between the range of to 25 ml for infants and the range of 450 to 500 ml for adults. It is also checked that the correct scale unit 11 is set since the graduation on the scale unit 11 will vary in dependence of the volume of the compression chamber in the embodiment according to FIGS. 1, 3 and 4. The spacing of the scale divisions on the volume scale 13 is dependent on the volume of the compression chamber and patient modules of the apparatus, while the spacing of the different scale divisions on the scale 12 are empirically determined. In the illustrative embodiment shown the compression module and the scale unit 11 have been formed for respirator ventilation of infants with a body weight of up to 40 kilos.

When the apparatus is started, first the displaceable scale unit 11 is adjusted in such a way that the body weight in question (scale 12) is set against the scale division cm H O on the pressure scale 10. For it has been empirically proved that this pressure of 20 cm H O will approximately correspond to the normal expansion of lungs of healthy children and also of healthy adults. After that the impulse generator IG is adjusted against the O-division on the scales 12 and 13. Subsequently, after the patient has been connected by means of a tracheal tube connected with the patient module, the pressure in the compression chamber module, when the valves KIV and PUV are closed and the separation or insufflation valve SV has been opened, will fall to the pressure P which is indicated on the manometer MM. After a few insufflation and exhalation cycles a steady state in the respirator ventilation is reached and at this stage the pressure P at the end of the exhalation phase may be checked and consequently also the volume reached by the single breath on the scale 13. If the obtained pressure P were to deviate significantly,

say by 5 cm H O from the expected final pressure 20 cm H O at the end of the exhalation phase and if the volume of the single breath were to deviate significantly from the volume desired. for the patient an adjustment of the calibration of the impulse generator IG and the scale unit 11 should be carried out so that the most convenient ventilation of the lungs is obtained. An increased ventilation is obtained when displacing the impulse generator and the scale unit 11 upwards and a decrease is obtained by moving them downwards along the pressure scale 10. By means of the shown arrangement the size of the single breath may be controlled and also established with great accuracy by reading the pressure P against the volume scale 13 on the scale unit l1.

The above procedure at the setting and control of the respirator corresponds to the two-pressure method mentioned above, although the patient module volume which is known has been integrated into the calculations at the graduation of the scales 12 and 13. If the volume of the patient module had not been integrated into these calculations, when using the two-pressure method, first pressure must be applied to the compression chamber module KRM while the separation valve SV is closed, whereby the impulse generator [G will close the inlet valve KIV of the compression chamber when the pressure P has been reached. The trachea] connection T is blocked at the tracheal tube after which the insufflation or separation valve SV will be opened, while the two valves KIV and PUV are kept closed. The pressure in the system will now fall somewhat to a pressure P (not shown), and the displaceable combined scale 11 (FIG. 4) will be adjusted in such a way that the O-divisions will be just opposite the pressure P for calibration of the apparatus. Since the compression chamber module KRM has a very great volume in relation to the patient module PM the pressure fall between the pressures P, and P will be only a few millimeters H O a pressure fall which is practically negligible. The necessary correction of the system if it is desired to avoid the necessity of checking two pressures and blocking the tracheal connection at the initial stage may be effected simply by displacing the index of the impulse generator relative to the sensing level of the impulse generator, so that the index will correspond to the pressure P and the sensing level will correspond to the pressure P In FIG. 3 the pressure variation curve in the compression chamber module has been indicated by a solid line and the pressure variation curve in the patient module has been indicatedby a dotted line. The pressure has been recorded on the ordinate and the time on the abscissa. It can clearly be seen how the pressure in the compression chamber module will fall and the pressure in the patient module and consequently the lungs of the patient will rise during the insufflation phase, until an equalization has been reached at the pressure P At the end of the insufflation phase, i.e. when the pressure P has been reached, the separation valve SV will be closed and after a short interval the exhalation valve PUV will be opened and also the inlet valve KIV, the exhalation being started and simultaneously the compression module being recharged. The exhalation phase is in the conventional way of considerably greater length than the insufflation phase, although the main portion of the pressure is discharged very quickly in the course of l to 2 s dependent on, among other things, the health condition of the lungs. The breathing rate is time controlled by means of the electronic impulse module ElM. An advantage of the apparatus is that the equalized pressure P will be very easy to determine in an exact way since said pressure is kept constant in the compression chamber module during the interval between the closure of the separation valve SV and the opening of the inlet valve KIV.

It will appear from the above that the driving apparatus of the respirator comprises a pressure chamber which is fed directly with the ordinary gas source and which is charged to a predetermined pressure relative to the desired volume of the single breath. Thereby the complex structure of known respirators has been obviated so that the apparatus will be considerably cheaper and simpler to manufacture.

What I claim is:

l. A method of operating a respirator for feeding pressurized gas into the lungs during an insufflation phase, after which the gas supply is interrupted and the gas is permitted to escape from the lungs during an exhalation phase, comprising the steps of feeding a predetermined gas volume, calculated on the basis of a desired insufflation volume of a single breath, into a closed compression chamber having rigid walls defining a constant volume and compressing said predetermined volume into said constant volume and increasing the pressure in the compression chamber to a pressure which is higher than the pressure prevailing at the end of the insufflation phase in a patient connection chamber of a substantially constant volume which is in open connection with the lungs of the patient, terminating any further flow of gas into said constant volume when said predetermined volume in said constant volume reaches said pressure, connecting the closed compression chamber which contains the compressed gas volume with the patient connection chamber for equalizing the pressures between the compression chamber and the patient connection chamber, and after said equalization of pressures disconnecting the compression chamber from the patient connection chamber and relieving the pressure in the patient connection chamber to the atmosphere at the same time initiating in the compression chamber a compression of a new gas volume for a suceeding insufflation phase.

2. A method according to claim 1 wherein the pressure to which the gas is compressed in the closed chamber is adjusted in dependence of the desired insufflation volume at one single breath.

3. A method according to claim 1, wherein the volume of the closed compression chamber into which the gas is compressed is adjustable in dependence upon the desired insufflation volume at a single breath of different patients but is maintained constant during treatment of any one patient.

4. An apparatus for operating a respirator having an inhalation phase and an exhalation phase comprising an insufflation valve; an exhalation valve; a patient connection unit connecting said insuffation valve to said exhalation valve; means for supplying pressurized gas to the lungs through the insufflation valve; said means for supplying pressurized gas to the lungs comprising a compression chamber having rigid walls defining a constant volume, a pressurized gas source, an inlet valve connecting said chamber to said pressurized gas source, said chamber being connected to said insufflation valve, a metering means connected with the compression chamber and adapted to determine the pressure therein, and control means associated with said metering means, said inlet valve, said insufflation valve and said exhalation valve for controlling said supply of pressurized gas to the patient connection unit via said compression chamber such that said control means causes said inlet valve and exhalation valve to open and causes said insufflation valve to close for an exhalation phase and upon sensing a predetermined pressure determined by said metering means, causes said insufflation valve to open and causes said inlet valve and said exhalation valve to close for an inhalation phase, thereby when the insufflation valve is open the compression chamber is of a fixed volume and the pressure therein is influenced only by the flow through the insufflation valve.

5. An apparatus according to claim 4, wherein the volume of the compression chamber is adjustable in dependence upon the desired size of a single breath of different patients, but can be maintained constant during treatment of any one patient. 

1. A method of operating a respirator for feeding pressurized gas into the lungs during an insufflation phase, after which the gas supply is interrupted and the gas is permitted to escape from the lungs during an exhalation phase, comprising the steps of feeding a predetermined gas volume, calculated on the basis of a desired insufflation volume of a single breath, into a closed compression chamber having rigid walls defining a constant volume and compressing said predetermined volume into said constant volume and increasing the pressure in the compression chamber to a pressure which is higher than the pRessure prevailing at the end of the insufflation phase in a patient connection chamber of a substantially constant volume which is in open connection with the lungs of the patient, terminating any further flow of gas into said constant volume when said predetermined volume in said constant volume reaches said pressure, connecting the closed compression chamber which contains the compressed gas volume with the patient connection chamber for equalizing the pressures between the compression chamber and the patient connection chamber, and after said equalization of pressures disconnecting the compression chamber from the patient connection chamber and relieving the pressure in the patient connection chamber to the atmosphere at the same time initiating in the compression chamber a compression of a new gas volume for a suceeding insufflation phase.
 2. A method according to claim 1 wherein the pressure to which the gas is compressed in the closed chamber is adjusted in dependence of the desired insufflation volume at one single breath.
 3. A method according to claim 1, wherein the volume of the closed compression chamber into which the gas is compressed is adjustable in dependence upon the desired insufflation volume at a single breath of different patients but is maintained constant during treatment of any one patient.
 4. An apparatus for operating a respirator having an inhalation phase and an exhalation phase comprising an insufflation valve; an exhalation valve; a patient connection unit connecting said insuffation valve to said exhalation valve; means for supplying pressurized gas to the lungs through the insufflation valve; said means for supplying pressurized gas to the lungs comprising a compression chamber having rigid walls defining a constant volume, a pressurized gas source, an inlet valve connecting said chamber to said pressurized gas source, said chamber being connected to said insufflation valve, a metering means connected with the compression chamber and adapted to determine the pressure therein, and control means associated with said metering means, said inlet valve, said insufflation valve and said exhalation valve for controlling said supply of pressurized gas to the patient connection unit via said compression chamber such that said control means causes said inlet valve and exhalation valve to open and causes said insufflation valve to close for an exhalation phase and upon sensing a predetermined pressure determined by said metering means, causes said insufflation valve to open and causes said inlet valve and said exhalation valve to close for an inhalation phase, thereby when the insufflation valve is open the compression chamber is of a fixed volume and the pressure therein is influenced only by the flow through the insufflation valve.
 5. An apparatus according to claim 4, wherein the volume of the compression chamber is adjustable in dependence upon the desired size of a single breath of different patients, but can be maintained constant during treatment of any one patient. 